Leading doctors have issued a stark warning that women should become mothers by the age of 35 or face a greater risk of infertility, miscarriage and health problems during pregnancy.

The Royal College of Obstetricians and Gynaecologists (RCOG) is urging would-be mothers to have children between the ages of 20 and 35 to minimise the chances of childbirth damaging their own or their baby's health.

It has issued its clearest advice yet on older motherhood, after doctors raised concerns that among the record number of women choosing later parenthood, some are ending up childless because they have ignored their biological clock and left it too late to start a family.

"Delay in childbirth is associated with worsening reproductive outcomes: more infertility and medical co-morbidity, and an increase in maternal and foetal morbidity and mortality," said the college, which represents the UK's 5,148 specialists in childbirth and women's health. "Women who start their family in their 20s or complete it by age 35 face significantly reduced risks."

While women who delayed childbearing should be supported, "they also need to know how fertility and pregnancy outcomes change with age. Biologically, the optimum period for childbearing is between 20 and 35 years of age. Both women and society need to be aware of the possible problems that older mothers may encounter," added the college.

RCOG spokeswoman Melanie Davies, a consultant at University College Hospital in London, said that a woman aged over 40 was between two and three times more likely to lose a baby, for example.

"Our statement has been prompted by concern among obstetricians and gynaecologists because we are seeing more and more [older] women who are confronting the heartbreak of infertility and miscarriage," said Davies. "Every week in my clinic I see women who say 'if only I had known this, I could have planned for this. I wouldn't have postponed my plans for pregnancy'."

The college fears too many women still do not understand that their fertility declines after 35. It wants the NHS and the Department of Health to start alerting the public to the fact that deferred childbirth can mean fertility or pregnancy complications. Schools, colleges, GPs' surgeries, family-planning centres and sexual-health clinics should all issue information to help "ensure that women are aware that, biologically, the best age for childbearing is 20-35 years", said the college.

In addition, GPs and other health professionals should talk to all women over 30 about the effects of ageing on fertility when they talk to them about contraception, for instance, it said.

But the Royal College of Midwives defended women's right to have children as late as their 40s. "We support women in their choice to have a baby in their late 30s and 40s, although pregnancy complications can be more common in older women. They have higher rates of induction of labour and Caesarean births, which present greater risks to both mother and baby. Despite this, we support a woman's decision to choose when to embark upon a pregnancy."

And Susan Seenan of Infertility Network UK, which supports couples who have fertility problems, said: "Delaying having children until you are in your 30s is a choice many women make, and in fact often they are not in a position to have children earlier in life."

However, such women should be aware of "the added problems when trying to conceive, particularly over the age of 35, and should understand that using fertility treatment is not a guarantee of success," she added.

Mary Newburn of the National Childbirth Trust, agreed that women needed "balanced information about the additional risks" of older motherhood. Earlier career breaks for women would help, while shared parental leave should help them feel less under pressure about achieving a certain level of career success before giving birth, she added.